This invention relates to a piping structure and in particular relates to the structure of a joint portion between pipes.
As one of conventional refrigerating apparatus, there has been known a multi-type air conditioner as disclosed in Japanese Patent Application Laid-Open Gazette No. 4-208370, in which a plurality of indoor units are connected to a single outdoor unit. In this air conditioner, a refrigerant circuit of the outdoor unit is connected to a refrigerant circuit of each of the indoor units through a connection pipe thereby forming a refrigerant piping system.
For the above-mentioned air conditioner, the outdoor unit and the indoor units are shipped from production facilities, are carried to the site of installation in a building or the like, are installed and are then connected to the connection pipe.
The connection pipe is formed in a way of brazing both pipes which each have a specific length and are each made of a copper pipe with each other. At the time, nitrogen is poured into the connection pipe to remove air out of the connection pipe so that air in the connection pipe is wholly displaced by nitrogen, and thereafter both the pipes are brazed.
Problems to be Solved
Each pipe of the air conditioner is formed, for example, in a uniform diameter from one opening end to another opening end and as mentioned above, the connection pipe is formed by brazing the pipes.
Meanwhile, in pipe connecting work, some general rules must be strictly observed. The general rules include "clean rule" and "dry rule". The dry rule is a rule that makes pipe connecting work so as not to leave water in the pipe. The clean rule is a rule that makes pipe connecting work so as to prevent the entry of alien substances into the pipe.
However, in conventional pipe connecting work, sufficient parts management is not necessarily made. For example, water drops due to dew fall or the like are often left on the inner surface of an original pipe for pipe connecting work. In other words, the pipe is often stored with both opening ends open.
Therefore, the pipe causing dew fall may be used as it is. Further, air in the pipe includes moisture. Accordingly, water may be left in the pipe contrary to the dry rule when refrigerant is charged into the pipe. This causes a problem of lack of reliability of air conditioning.
Furthermore, when the pipe is heated by a burner or the like in brazing, air in the pipe may produce an oxide film on the surface of the pipe made of a copper pipe.
Such a phenomenon is contrary to the clean rule. In detail, when refrigerant is charged into the pipe, the refrigerant peels off the oxide film. The peeled oxide film may blockade a narrow space such as a capillary tube or may pollute a lubricating oil for refrigerating apparatus thereby degrading lubricating performance. This may cause a problem leading to breakage of equipment.
The present invention has been made in view of the foregoing problems and therefore has an object of enabling strict observation of both the clean rule and the dry rule in pipe connecting work thereby enhancing the reliability of air conditioning.